The invention relates generally to bearings and, more particularly, bi-directional tilting pad thrust bearings arrangements.
Rotational bearings are very well known in the art to provide an interface between a rotating structure and a contact surface. It is common to employ some type of pad or pads at the interface to optimize the interconnection between the bearing and the rotating structure and to transmit axial thrust forces.
Load capacity is highly dependent on the pad interface in a bearing. It has been found that the interface can be further optimized, for better transmission of axial thrust forces, by tilting the pads of a bearing to reduce the amount of friction. Such increasing load capacity by reduced friction is achieved by controlled hydroplaning. Such tilting pad thrust bearing arrangements are well known in the art. Typically, such tilting pads arrangements include an array of fixed pads that are all tilted in a given rotational direction, such as a forward rotational direction. This is advantageous in that hydroplaning can be achieved.
It is also known that offsetting the tilt of the thrust pads can further optimize bearing performance. For example, offsetting the pivot angle of the thrust pad desirably increases load capacity as seen in the graph of FIG. 9. Studies have found that offset pivoting pads in the direction of rotation can generate, for example, 50-100 percent additional load capacity for the thrust bearing. Therefore, it is highly desirable to offset the pivot tilt of a thrust bearing.
A serious drawback of tilted or angled pad thrust bearing arrangements is that while rotation in the forward direction is highly optimized, rotation in the reverse direction is extremely inefficient as the tilted pads are only optimized in the forward direction. However, since reverse directional rotation is frequently needed in many different bearing environments, there is a need for a thrust bearing that is bi-directional while still providing the optimizing hydroplaning of tilting thrust pads.
There have been many attempts in the prior art to provide a bi-directional thrust bearing with tilting pads. Such bearing includes pads that can rock back and forth about a longitudinal axis that pass through the center axis of rotation of the device. These prior art tilting pads are fixed in place relative to some type of fulcrum, which is either provided on the underside of the pad itself or on some type of carrier on which the pad rests. For example, it is well known in the art to provide a fixed tilting pad that has a 50/50 percent tilt on its leading edge and its trailing edge. When the device is rotated in a forward direction, the pads automatically tilt to provide the desirable hydroplaning and increased load capacity. When the rotation is reversed, the pads automatically tilt in the opposite direction to provide the desired hydroplaning and increased load capacity. In this case, a 50/50 leading edge tilt in both directions is required to ensure equal load capacity in both the forward and reverse directions.
However, it should be noted that the desirable offset tilting is not well-suited in such a bi-directional fixed tilting pad arrangement, as described above. This is because an optimized tilting offset can only be optimized in only one direction, e.g. the forward rotational direction, when the pad is fixed in place. In that case, when the rotation is reversed, the same fixed offset will greatly detrimentally effect load capacity in that reverse direction. Therefore, bi-directional tilting pad thrust bearing arrangements typically cannot use any type of optimized offset tilt and must use a 50/50 fulcrum positioning for equally tilt in both the forward and reverse rotational directions. Therefore, such bearing arrangement must sacrifice the improvements capable from offset tilting in order to make the bearing bi-directional and maintain good load capacity in both rotational directions.
Therefore, it is not possible for a thrust bearing structure to be both bi-directional and optimized with offset tilt in both the forward and reverse directions at the same time.
In view of the foregoing, there is a demand for thrust bearing arrangement to have an optimized bearing surface.
There is a demand for a bearing to have an increased load capacity.
There is a further demand for a single bearing arrangement that can be used for both forward and reverse rotation thereby obviating the need for stocking multiple bearing for multiple rotation directions.
There is a demand for a bearing arrangement that enables rotation of a given device to be reversed without the need for changing the bearing in order to maintain optimal load capacity.
There is a demand for a bearing that is bi-directional.
There is a demand for a bearing that has a rotation offset pivot.
There is yet another demand to provide a bearing that maintains an offset pivot tilt regardless of the direction of rotation of the bearing.